The present invention relates in general to producing crude oil from small, low or non flowing wells and more particularly to a safe new improved technology for producing more oil from these wells at lower cost than the prior art.
The common way of producing oil from these wells is to lower steel tubing down into the well casing just above the perforations with the outer portion of a pump connected to the bottom end of the tubing. Then lower steel rod down into the tubing with the inner portion of the pump connected to its bottom end until the two portions of the pump mate. To pump the oil from the well into the tubing the rod is moved up and down about the length of the pump (an average of about three feet) by the electric powered pump jack at the wellhead. This method has many disadvantages; one of the important ones is that when the pump is unable to pump oil out of the well for almost any reason the whole string of rod and tubing has to be pulled back out of the well to repair the equipment. On the average these wells are about two thousand feet deep and the pieces of rod and tubing are screwed together about every twenty five to thirty feet. This requires a large rig (truck) with at least a forty foot retractable boom and a place to store, in a vertical position, about one hundred pieces of rod and tubing while the equipment is being repaired.
Another important disadvantage is that when crude oil starts to cool down solids start to precipitate from the liquid and clog up the passage ways for the oil to seep out of the formation, through the perforations in the casing, and into the well, slowing down the production. The oil in the formation is normally very hot and all in liquid form but, the steel rod and tubing that is left in the well full time cools down the oil in the bottom of the well by conducting heat to the surface much faster than the gas or oil it replaced.
Attempts have been made to produce oil using a method called “swabbing”. This is accomplished by lowering a rubber cup seal (swab cup) on a mandrel down into the oil in a well on the end of a cable wound on a power winch at the well head; then pulling the cable, swab, and the oil up to the surface. This method is simple and does increase production but there are problems with the equipment that keep it from being practical.
The design of the cup seal used on the prior art oil well swabs comes from the cup seals used in hydraulic equipment but the application is very different. In hydraulic power equipment the cup seal moves along a smooth surface and is not usually required to move in the direction of the lip when under high pressure. Using a cup seal to pull a tall column of oil out of a rough well casing in the direction of its lip is obviously the wrong application for the following reasons.
The swab can be very hard on old well casing when it is pulling a tall column of oil out of the well. The pressure on the lip of the swab cup from the column of oil above and the friction against the rough casing causes the lip to exert a very large outward force on the inside wall of the casing. This can cause a break in the casing in the area of the salt water formations where it has been weakened by heavy corrosion from the outside. Also in some cases the large outward force on the wall of the casing by the lip can cause it to partially turn back under the base and stick the swab in the casing where it is almost impossible and very expensive to fish out.
The casing in the well is also screwed together about every thirty feet with couplings as it is dropped into the well hole before it is cemented into the earth which often leaves a small space between the ends of the casing large enough to catch the lip of the swab and stick it in the well casing, even with a short column of oil above it. When any of the above problems happen that can't be corrected the well usually has to be taken out of production and permanently plugged, which is a very expensive operation.